Gametogenesis in females is controlled by follicle-stimulating hormone (FSH) from the pituitary, which is, in turn, regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH regulates FSH synthesis through induction of the immediate early gene, c-Fos, which, upon heterodimerization with c-Jun, creates an AP-1 transcription factor that binds the promoter of the FSH 2-subunit gene. The overall goal of this application is to ascertain the mechanism of GnRH induction of c-Fos and to elucidate the role of AP-1 in the gonadotrope in vivo. AP-1 is the only factor known to be involved in the induction of the FSH 2-subunit gene by GnRH. c-Fos, the most highly GnRH-induced gene in the gonadotrope, is the most regulated AP-1 isoform, while c-Jun expression varies less with hormone treatment. The molecular mechanism of c-Fos induction by GnRH in the gonadotrope cell is not known. Neither has a role for AP-1 in reproduction in vivo been determined. Herein, I will utilize novel approaches to delineate the mechanisms underlying the regulation of c- Fos expression by GnRH. In the first aim, I will determine the molecular mechanism of c-Fos induction by GnRH. In the second aim, I will determine the regulation of protein stability and degradation, since c-Fos is an immediate-early gene with a very unstable message and labile protein, and its cellular concentration is controlled on the level of turnover, as much as on the level of expression. In the third aim of this proposal, I will determine the function of AP-1 in reproduction in vivo with the use of genetically modified animals. First, I will assess reproductive function and gonadotropin expression in c-Fos deficient animals and then, as complementary approach, use mice that lack c-Jun specifically in the pituitary gonadotrope. Jun isoforms are obligatory heterodimeric partners for Fos isoforms, whose interaction creates an AP-1 transcription factor that binds DNA. c-Jun, in particular, is essential for development, since knock-out animals die in utero, and with the use of CRE-lox system, I will analyze the function of c-Jun in gonadotrope in vivo. Results obtained from these studies will make substantial contributions to our understanding of the molecular mechanisms that affect gene expression in the gonadotrope and provide insight into the physiology and pathophysiology of the mammalian reproductive system. I propose to expand our understanding of molecular mechanisms of GnRH induction of c- Fos gene in the gonadotrope in a cell culture model, which will lead to a better understanding of GnRH regulation of gene expression in the pituitary, and the function of AP-1 in vivo, utilizing genetically modified mice.